1. Field of the Invention
The present invention relates to a resist cover film forming material that is suitably used for the manufacture of an immersion exposure resist cover film that serves to protect a resist film against a medium (liquid) in the immersion exposure technology and that has a high ArF excimer laser and/or F2 excimer laser transmittance, the immersion exposure technology intending to achieve an improved resolution by filling the gap created between the projection lens of an exposure device and a wafer with a medium having a refraction index (n) of greater than 1 (the value for air); a resist pattern forming method using the resist cover film forming material; and an electronic device and a manufacturing method for the same.
2. Description of the Related Art
In recent years semiconductor integrated circuits have been highly integrated, with minimum linewidths being reduced to as small as 100 nm or less. Fine patterns have conventionally been obtained for instance by a method that comprises the steps of covering a thin film-deposited work surface with a resist film, selectively exposing the resist film, developing the resist film to form a resist pattern, performing dry etching using the resist pattern as a mask, and removing the resist pattern to form a desired pattern in the workpiece.
It is required for the achievement of finer patterns to shorten the wavelength of the exposure light and to develop a resist material that is suitable for the characteristics of the exposure light for a high-resolution pattern. Improvement on an exposure device for a shorter exposure light wavelength, however, has met with difficulty because of enormous development costs. In recent years an ArF (argon fluoride) excimer laser with a wavelength of 193 nm has been extensively put into practice use as a next generation exposure light source, replacing a conventional KrF (krypton fluoride) excimer laser having a wavelength of 248 nm. Accordingly, ArF excimer laser-equipped exposure devices are now on the market; however, they are still fairly expensive. Moreover, developments for resist materials to which exposure light of shorter wavelengths can be applied are not also easy, and as such these resist materials have not therefore been provided yet. For this reason, it has been difficult for the conventional resist pattern forming method to provide finer patterns.
The immersion exposure technology has become a focus of attention as an up-to-date exposure technology. With this technology an increased resolution can be obtained by filling the gap, created between the projection lens of a stepper and a wafer, with a medium (liquid) with a refraction index of greater than 1 (the value for air). The resolution of the stepper can be generally represented by the formula “resolution=k (process factor)×λ(wavelength)/NA (numerical aperture)”; the shorter the wavelength and the greater the NA of the projection lens, the greater the resolution. NA is obtained by “NA=n×sin α” where “n” is a refraction index of medium through which exposure light passes and “α” is the maximum incident angle of the exposure light. Since the exposure step in the conventional pattern forming method is conducted in the air, the refraction index of medium is 1. The immersion exposure technology, on the other hand, utilizes between the projection lens and a wafer a liquid with a refraction index of greater than 1. This increases “n” in the NA formula and thereby the minimum resolvable dimension can be reduced by a factor of “n” provided “α” is constant. In addition, there is an advantage that “α” can be reduced and depth of focus (DOF) can be increased by a factor of “n” provided NA is constant.
Such an immersion technology that involves the use of liquid with a refraction index that is greater than that of air has been a known technology in the field of microscopes, however its application to the fine processing technology has been made only by proposing an exposure device in which liquid is placed between a lens and a wafer, the liquid having a refraction index that is substantially equal to or slightly smaller than that of the lens (see Japanese Patent Application Laid-Open (JP-A) No. 62-065326). Because attempts to apply the immersion technology to the fine processing technology started just in the last few years, the current situation is that problems are gradually emerging with respect to the immersion exposure device and resist materials used in this device.
One of the foregoing problems is a situation where a resist film is exposed to liquid (e.g., water) filling up the gap between the projection lens and a wafer, releasing an acidic ingredient, generated in the resist film upon exposure, into the liquid to result in poor resist sensitivity. In addition, when the water-infiltrated resist film is exposed to an excimer laser, certain chemical reactions may occur that impair the resist's original performance and that soils the projection lens by degasification. The dirt on the lens is problematic because it results in exposure failure and poor resolving power.
Although a strategy that aims to form a resist cover film over the upper surface of the resist film has been considered in order to overcome these problems, this strategy has met with difficulty in forming such a resist cover film without dissolving therein the resist film and without causing the resist cover film to mix with the resist film. In addition, both the ArF excimer laser of 193 nm wavelength and the F2 excimer laser beam of 157 nm wavelength, the latter of which is much shorter than the ArF excimer laser in wavelength, do not pass through general organic materials. For this reason, the range of available materials for the resist cover film is extremely small. Even when it succeeded in obtaining such a material, this material does not dissolve in alkali general developers. Accordingly, the resist cover film needs to be removed prior to development by use of a remover specifically designed for the resist cover film. It is also required to ensure the primary purpose of preventing the elution of unwanted resist ingredients in the exposure medium
Accordingly, any material that can be used for the manufacture of an immersion exposure resist cover film has not yet been provided, which the resist cover film is capable of being formed on a resist film without dissolving therein the resist film, of preventing elution of ingredients of the resist film in a liquid with a high refraction index that fills up the gap between the projection lens of an exposure device and a wafer and infiltration of the liquid into the resist film, and of being removed readily; which never impairs the original resist performance; and which has a high ArF and F2 excimer lasers transmittance. Furthermore, no related technology has been provided that utilizes this material. Thus, developments of this technology have been demanded.
It is an object of the present invention to solve the foregoing problems and to achieve the objects described below.
That is, an object of the present invention is to provide a resist cover film forming material that is suitably used for the manufacture of an exposure immersion resist cover film used to protect a resist film against a medium in the immersion exposure technology and that has a high ArF excimer laser and/or F2 excimer laser transmittance, the immersion exposure technology intending to achieve an improved resolution by filling the gap created between the projection lens of an exposure device and a wafer with a medium having a refraction index (n) of greater than 1 (the value for air).
Another object of the present invention is to provide a resist pattern forming method capable of high-resolution immersion exposure by protecting the resist film against the liquid and by preventing the generation of dirt on the lens without impairing the resist film performance, for achieving efficient and easy formation of a fine, high-resolution resist pattern.
Still another object of the present invention is to provide a method for manufacturing an electronic device, which the method is capable of formation of a fine, high-resolution resist pattern by means of immersion exposure without impairing the resist pattern performance and of efficient mass production of a high-performance electronic device having a fine interconnection pattern formed using the resist pattern, and a high performance electronic device such as a semiconductor device, which has a fine interconnection pattern and manufactured using this manufacturing method.